The objective of the proposed project is to continue our investigations on the mechanism of action and physiological significance of the neural cell adhesion molecule N-CAM during vertebrate embryogenesis. These studies are designed to define more fully the molecular structure of N-CAM and of cell-cell bonds, and to relate the chemical properties of N-CAM to its function in tissue morphogenesis and formation of nerve tracts. In addition to preparation of molecular reagents required for this work, the specific aims for the next five years include: 1) the description of structural features and molecular interactions that are required for neural cell-cell binding, 2) a comparison of N-CAM expression and structure in different tissues and developmental stages, 3) studies on the formation, structure and biological consequences of nerve bundling and branching, 4) a further evaluation of the role of N-CAM in muscle development and nerve-muscle interactions, and 5) the use of antibodies to characterize and perturb N-CAM during early stages of embryogenesis. These studies will involve experiments with embryos, tissues, cells, membrane vesicles, and purified cell surface molecules. Rabbit antisera and mouse monoclonal antibodies will be used extensively for the characterization of N-CAM, and for inhibition of its function in cultures and in vivo. Evaluation of the biological consequences of N-CAM mediated adhesion will involve phase, immunofluorescence and electron microscopy, combined with serial reconstructural computer graphics and techniques for labeling neuronal tracts. Previous work on N-CAM already indicates that this molecule is expressed during many phases of development, and is associated with a variety of tissues that undergo rapid remodeling. It is hoped that the proposed studies will lead to a more refined description of the molecular and cellular events associated with cell-cell adhesion, and consequently a more fundamental understanding of tissue formation during embryogenesis.